Surface Water in Idaho

Idaho has more than 95,000 miles of rivers and streams and 100 lakes and reservoirs, making water one of the state's most important resources. Our rivers, lakes, streams, reservoirs, and wetlands not only provide great natural beauty but also supply the water necessary for drinking, recreation, industry, agriculture, and aquatic life.

DEQ's Surface Water Program is responsible for ensuring Idaho's streams, rivers, lakes, reservoirs, and wetlands meet their beneficial uses and Idaho water quality standards.

Continuing Planning Process

As the agency tasked with implementing the federal Clean Water Act in Idaho, DEQ is required by section 303(e) of the act to develop a Continuing Planning Process (CPP) that describes the ongoing processes and planning requirements of the state's water quality program. One tool DEQ uses to implement its water quality program is its Water Quality Management Plan. In essence, the plan is a compilation of the guidance and programs DEQ uses to implement the Clean Water Act. Learn more.

Water Quality Standards

DEQ uses water quality standards to know if it is adequately protecting Idaho's water. A water quality standard defines the goals that have been set for a water body by designating the uses for the water, sets criteria necessary to protect those uses, and prevents degradation of water quality. Learn more.

Beneficial Uses

Beneficial uses are the desired uses that water bodies should support. Beneficial uses include water supply (domestic, agricultural, and industrial); recreation (such as swimming, boating, and fishing); and aquatic life. Each beneficial use has a unique set of water quality requirements or criteria that must be met for the use to be supported. Most water bodies have multiple beneficial uses. A water body is considered impaired when it does not meet the water quality criteria needed to support one or more of its beneficial uses. Learn more.

Antidegradation Guidance Under Development

Antidegradation describes policies designed primarily to maintain water quality where it meets or exceeds levels necessary to support beneficial uses. Federal water quality standards require Idaho to establish a three-tiered antidegradation program. Learn more.

Water Quality Criteria

Idaho's water quality standards prescribe certain criteria that must be met to ensure the beneficial uses of the state's surface waters are supported. These criteria can be numeric or narrative. Learn more.

Mercury

Mercury is a naturally occurring metallic element that is found in trace amounts in air, water, and soil. Mercury is toxic to both aquatic life and humans, but its toxicity is primarily a human health concern. By far the most common route of mercury exposure in humans is eating fish and shellfish contaminated by methylmercury, according to the federal Centers for Disease Control. Learn more about mercury in surface water and what DEQ is doing to address this contaminant here.

Temperature

Water temperature is a key factor in the health of fish and other coldwater organisms. Warm water can stress and eventually kill coldwater fish such as salmon and trout. The incubating eggs and sac fry of salmonid fishes are particularly sensitive to increases in water temperature. Warm water can also make other water quality problems worse. For instance, it can favor bacteria and nuisance aquatic plant growth and intensify water chemistry problems involving dissolved oxygen and ammonia. An increase in stream temperatures may reflect other stream health problems as well, such as loss of riparian vegetation, eroding streambanks, and excessive sedimentation. Idaho's water temperature standards are designed to protect aquatic life uses. Learn more.

Monitoring and Assessment

As the agency responsible for protecting Idaho's surface water, DEQ continually monitors and assesses the quality of the state's rivers, streams, and lakes. This information is used to report to the US Environmental Protection Agency and to make decisions regarding water quality management. Learn more.

Nonpoint Source Pollution

Unlike pollution that is discharged directly from a pipe into surface waters, nonpoint source pollution generally does not have a single point of origin. Nonpoint source pollutants can be natural, such as sediment, or human-made, such as chemicals and toxics. They are generally created in or on the land and carried off by stormwater runoff when it rains or snowmelt. Nonpoint source pollution can damage fish, wildlife, and their habitat; promote excessive weed growth; generate odors; and degrade Idaho's scenic beauty and recreational opportunities. Learn more.

Total Maximum Daily Loads

When water bodies don't meet water quality standards, DEQ develops total maximum daily loads, or TMDLs, to improve water quality. A TMDL establishes the maximum amount of a pollutant that a water body can receive and still meet water quality standards. This pollutant budget is expressed in terms of loads: the amounts of pollutants added to a water body during a given time or per a volume of water. Learn more.